Electrode for electrochemical device and electrochemical device

ABSTRACT

An electrode for an electrochemical device, including an elongated collector, a lead provided halfway along a longitudinal direction of the collector, and active material layers provided on the collector, wherein when L a  (m) is a distance from one end of the collector, in the longitudinal direction, up to the lead, and L b  (m) is a distance from the other end of the collector, in the longitudinal direction, up to the lead, and ρ (Ωm) is a resistivity of the collector at 25°, where L opt  (m) being 1.9×10 6 ρ, the L a  (m) and L b  (m) are from 0.95 L opt  to 1.05 L opt  respectively.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electrode for electrochemicaldevices, and to an electrochemical device.

2. Related Background Art

Spirally wound electrochemical devices are formed by winding electrodesin the longitudinal direction, the electrodes being obtained by formingactive material layers on an elongated collector. When the length of thecollector in the longitudinal direction is substantial, the collector isprovided with a plurality of leads, spaced apart from each other, in thelongitudinal direction of the collector, in order to suppress heatgeneration, polarization and the like that result from concentration oflarge currents (see, for instance, Japanese Patent Application Laid-openNos. H7-192717, H11-283882, H11-283883, H11-317218, 2000-106167,2000-182656, 2000-110453, 2006-260892 and 2006-286404).

SUMMARY OF THE INVENTION

During winding, same-polarity leads have conventionally been disposed onthe collector overlapping substantially with each other, without payingspecial attention to the arrangement spacing between leads or to thenumber of leads thus arranged. To be used with greater efficiency, theelectrochemical device must exhibit lower impedance. In terms oflowering the impedance of the electrochemical device, it may presumablysuffice to reduce the contribution of the collector to resistance, bysimply increasing the number of leads and narrowing the lead arrangementspacing.

However, the inventors have found that leakage current increases whenthe lead arrangement spacing is too narrow. An increase in leakagecurrent is accompanied by energy loss, and is thus undesirable. That is,the inventors have found that there is a suitable range for the leadarrangement spacing.

On the basis of the above finding, it is an object of the presentinvention to provide an electrode for electrochemical devices thatallows reducing both impedance and leakage current, and to provide anelectrochemical device using the electrode for electrochemical devices.

The electrode for an electrochemical device according to the presentinvention comprises an elongated collector, a lead provided halfwayalong a longitudinal direction of the collector, and an active materiallayer provided on the collector.

When L_(a) (m) is a distance from one end of the collector, in thelongitudinal direction, up to said lead, L_(b) (m) is a distance fromthe other end of the collector, in the longitudinal direction, up to thelead, and ρ (Ωm) is a resistivity of the collector at 25° C., whereL_(opt) (m) being 1.9×10⁶ρ, the L_(a) (m) and L_(b) (m) are from 0.95L_(opt) to 1.05 L_(opt) respectively.

Another electrode for an electrochemical device according to the presentinvention comprises an elongated collector, n leads (n being an integerequal to 2 or greater) provided spaced apart from each other in thecollector, in a longitudinal direction of the collector, and an activematerial layer provided on the collector.

When L_(a) (m) is a distance from one end of the collector, in tielongitudinal direction, up to a lead closest to the one end, L_(b) (m)is a distance from the other end of tie collector, in the longitudinaldirection, up to a lead closest to the other end, L₁, L₂, . . . ,L_(n−1) (m) are distances between adjacent leads, and ρ (Ωm) is aresistivity of the collector at 25° C., where L_(opt) (m) being1.9×10⁶ρ, the L_(a) and L_(b) are from 0.95 L_(opt) to 1.05 L_(opt)respectively, and (L₁/2), (L₂/2), . . . , (L_(n−1)/2) respectively rangefrom 0.95 L_(opt) to 1.05 L_(opt).

The electrochemical device according to the present invention comprisesa pair of electrodes, both electrodes being the above-describedelectrode for electrochemical devices.

Such an electrode for electrochemical devices affords an electrochemicaldevice having low impedance and low leakage current.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective-view diagram of an electrode forelectrochemical devices according to a first embodiment;

FIG. 2 is a schematic perspective-view diagram of an electrode forelectrochemical devices according to a second embodiment;

FIG. 3 is a schematic perspective-view diagram of an electrode forelectrochemical devices according to a third embodiment;

FIG. 4 is a schematic perspective-view diagram of an electrode forelectrochemical devices according to a fourth embodiment;

FIG. 5 is a partial-cutaway schematic perspective-view diagramillustrating an example of an electrochemical device according to anembodiment of the present invention;

FIG. 6 is a partial-cutaway schematic perspective-view diagramillustrating another example of an electrochemical device according toan embodiment of the present invention; and

FIG. 7 is a table listing conditions and results in examples andcomparative examples.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention are explained in detailbelow with reference to accompanying drawings. In the drawings,identical or equivalent elements are denoted with identical referencenumerals, and recurrent explanations thereof are omitted. Thedimensional ratios in the drawings do not necessarily match actualdimensional ratios.

First Embodiment

An electrode for electrochemical devices 10 according to a firstembodiment will be explained with reference to FIG. 1. The electrode forelectrochemical devices 10 comprises mainly a collector 12, activematerial layers 13A, 13C containing an active material, and a lead 15.

The collector 12 is a conductive member in the form of a rectangularelongated plate. Although not particularly limited thereto, the materialof the collector is preferably a metallic material, such as copper,aluminum or nickel. For instance, the electric resistivity ρ of copper,aluminum and nickel are 1.68×10⁻⁸ Ωm, 2.65×10⁻⁸ Ωm, 6.99×10⁻⁸ Ωm,respectively. The thickness of the collector is not particularlylimited, and may range from 10 to 50 μm. Also, the length L₀ in thelongitudinal direction and the length W₀ in the direction (widthdirection) perpendicular to the longitudinal direction are notparticularly limited. The length L₀ in the longitudinal direction mayrange, for instance, from 80 to 150 mm, while the length W₀ in the widthdirection may range, for instance, from 12 to 16 mm. The aspect ratio(L₀/W₀) of the collector is preferably 5 to 10, more preferably about7.0

The lead 15 is a conductive member that plays the role of current inputterminal in the collector 12. The lead 15 is shaped as a rectangularplate, the longitudinal direction of the lead 15 being perpendicular tothe longitudinal direction of the collector 12. In the presentembodiment, one end face 15 d of the lead 15 in the longitudinaldirection extends up to one side face 12 d of the collector 12 in thedirection (width direction) perpendicular to the longitudinal directionof the collector 12, while the other end face 15 c of the lead 15, inthe longitudinal direction, extends beyond the other side face 12 c ofthe collector 12 in a direction (width direction) that is perpendicularto the longitudinal direction of the collector 12. The thickness of thelead 15 is not particularly limited, and may be for instance similar tothat of the collector 12. The length of the lead 15 in the longitudinaldirection can be arbitrarily set in accordance with the way in which thelead is to be used, provided that the other end face 15 c of the lead 15protrudes beyond the side face 12 c of the collector 12. The length A ofthe lead 15, in a direction perpendicular to the longitudinal directionof the lead 15, is best sufficiently shorter than the length L₀ of thecollector 12 in the longitudinal direction of the latter. For instance,the lead 15 may protrude about 10 to 25 mm beyond the side face 12 c ofthe collector 12, and the width A of the lead 15 may range, forinstance, from 2 to 10 mm.

The lead 15 and the collector 12 are fixed together and electricallyconnected by way of, for instance, a conductive adhesive, soldering orwelding. Side faces 15 a and 15 b of the lead 15 extending in thelongitudinal direction thereof are respectively parallel to end faces(one end, other end) 12 a, 12 b that are perpendicular to thelongitudinal direction of the collector 12.

The active material layers 13A, 13C, which are layers containing anactive material, are provided on the front and rear faces, respectively,of the collector 12. Specifically, the active material layer 13C isprovided over substantially the entire surface of the collector 12 wherethe lead 15 is not provided. Meanwhile, the active material layers 13A,13A are dividedly provided on the surface of the collector 12 on whichthe lead 15 is provided, at portions other than the portion at which thelead 15 is provided.

The active material layers 13A, 13C comprise preferably an activematerial and a binder. More preferably, the active material layers 13A,13C comprise a conduction enhancer.

Various active materials, not particularly limited, can be used asactive materials for positive electrodes of lithium-ion secondarybatteries, so long as the active material is capable of storing andreleasing lithium ions, desorbing and intercalating lithium ions, andallows reversible doping and dedoping of lithium ions and counter anionsof lithium ions (for instance, ClO₄ ⁻). The active material may be, forinstance, a lithium-containing metal oxide. Examples oflithium-containing metal oxides include, for instance, a lithium oxidecomprising at least one metal selected from the group consisting of Co,Ni and Mn, such as LiMO₂ (wherein M denotes Co, Ni or Mn) orLiCo_(x)Ni_(1-x)O₂, LiMn₂O₄ and LiCo_(x)Ni_(y)Mn_(1-x-y)O₂ (wherein xand y are greater than 0 and smaller than 1), lithium vanadium compound(LiV₂O₅) or olivine-like LiMPO₄ (wherein M denotes Co, Ni, Mn or Fe).

Various active materials, not particularly limited, can be used asactive materials for negative electrodes of lithium-ion secondarybatteries, so long as the active material is capable of storing andreleasing lithium ion, desorbing and intercalating lithium ions, andallows reversible doping and dedoping of lithium ions and counter anionsof lithium ions (for instance, ClO₄ ⁻). Examples include, for instance,natural graphite, artificial graphite, mesocarbon microbeads, mesocarbonfibers (MCF), coke, glass-like carbon, carbonaceous materials such asfired product of organic compounds or the like, metals that can combinewith lithium, such as Al, Si or Sn, or amorphous compounds having, as amain component, an oxide such as SiO₂ or SnO₂.

The electrodes for electric double-layer capacitors may be, forinstance, various porous materials having electron conductivity.Suitable examples include, for instance, natural graphite, artificialgraphite, mesocarbon microbeads, mesocarbon fibers (MCF), coke,glass-like carbon or carbonaceous materials such as fired products oforganic compounds or the like.

As the binder there may be used various bonding agents, not particularlylimited, provided that they can fix the above active material and,preferably also the conduction enhancer, to the collector. Examplesthereof include, for instance, a fluororesin such as polyvinylidenefluoride (PVDF) or polytetrafluoroethylene (PTFE), or a mixture ofstyrene-butadiene rubber (SBR) with a water-soluble polymer(carboxymethylcellulose, polyvinyl alcohol, sodium polyacrylate,dextrin, gluten and the like).

Examples of the conduction enhancer include, for instance, carbon black,metal micropowders of copper, nickel, stainless steel, iron or the like,mixtures of carbon materials and metal micropowders, or conductiveoxides such as ITO. The conduction enhancer is a material added with aview to increasing the electron conductivity of the active materiallayers 13A, 13C. Acetylene black or carbon black can be suitably used asthe conduction enhancer.

Conventional methods may be used for forming the active material layers13A, 13C. Although the active material layers 13A, 13C cover preferablymost of the regions on the front and rear faces of the collector 12, theactive material layers 13A, 13C need not necessarily cover all theregions, so that, for instance, the edges of the collector may remainuncovered.

In the present embodiment, the distance L_(a) between the lead 15 and anend face (one end) 12 a of the collector 12 in the longitudinaldirection, and the distance L_(b) between the lead 15 and an end face(other end) 12 b of the collector 12 in the longitudinal direction rangeboth from 0.95 L_(opt) to 1.05 L _(opt).

Herein, L_(opt) (m)=1.9×10⁶ρ, with ρ denoting the electric resistivity(Ωm) of the collector 12 at 25° C.

The distance L_(a) and the distance L_(b) can be thought of as themaximum distance covered by current in the collector 12 when current issupplied to, and discharged from, the active material layers 13A, 13Cvia the collector 12. Also, L_(opt) is the optimal value of this maximumdistance, and is determined by the electric resistivity of the collector12. In the present embodiment, therefore, the distance L_(a) and thedistance L_(b) range from 95 to 105% of the optimal value L_(opt).

An electrochemical device using such an electrode has enhancedcharacteristics, with extremely low impedance and leakage currentvalues. Leakage current tends to increase when the distances L_(a) andL_(b) are smaller than 0.95 L_(opt), while the impedance of theelectrochemical device tends to increase when the distances L_(a) andL_(b) exceed 1.05 L_(opt).

Second Embodiment

An electrode for electrochemical devices 10 according to a secondembodiment is explained next with reference to FIG. 2. The electrode forelectrochemical devices 10 according to the present embodiment differsfrom the electrode for electrochemical devices according to the firstembodiment in the shape of the lead 15, and thus only this feature willbe explained. In the lead 15 according to the second embodiment, the endface 15 d does not protrude up to the side face 12 d of the collector12, but is positioned over the surface 12 e of the collector 12. Such anelectrode for electrochemical devices 10 elicits the same effect as thatof the first embodiment.

Third Embodiment

An electrode for electrochemical devices 10 according to a embodiment isexplained next with reference to FIG. 3. The electrode forelectrochemical devices 10 according to the present embodiment differsfrom the electrode for electrochemical devices according to the firstembodiment in the shape of the lead 15, and thus only is feature will beexplained. The lead 15 according to the third embodiment is not providedon the front face or rear face of the collector 12 but on the side face12 d of the collector 12. As a result, the active material layer 13A isnot split but formed as a singe unit, as is the case with the activematerial layer 13C. Such a lead 15 can be easily formed by cutting thecollector 12 and the lead 15 out of a singe conductive plate. Such anelectrode for electrochemical devices 10 elicits the same effect as thatof the first embodiment.

Fourth Embodiment

An electrode for electrochemical devices 10 according to a fourthembodiment is explained next with reference to FIG. 4. In the electrodefor electrochemical devices 10 according to the present embodiment thelength of the collector 12 in the longitudinal direction is longer thanis the case in the electrode for electrochemical devices 10 of the firstembodiment. Also, there are provided n spaced-apart leads 15 in thelongitudinal direction of the collector 12, n being an integer equal to2 or higher. The n leads are sequentially denoted as 15 ₁, 15 ₂, . . . ,15 _(n), from the left of FIG. 4. The distances L_(a) and L_(b) aredefined in the same way as in the fist embodiment and lie within thesame ranges as prescribed in the first embodiment. Preferably, thenumber n is for instance about n=4.

Here, L₁ denotes the distance between adjacent leads 15 ₁, 15 ₂, L₂ thedistance between adjacent leads 15 ₂, 15 ₃, . . . and L_(n−1) thedistance between adjacent leads lead 15 _(n−1), 15 _(n). In the presentembodiment, the distances L₁,L₂, . . . , L_(n−1) are set so as tosatisfy the condition that (L₁/2),(L₂/2), . . . , (L_(n−1)/2) range allfrom 0.95 L_(opt) to 1.05 L_(opt).

As is the case with L_(a) and L_(b) in the first embodiment,(L₁/2),(L₂/2), . . . , (L_(n−1)/2) can be thought of as the maximumdistances covered by the current in the collector 12 when current issupplied to, and charging is carried out in, the electrode 10. Also,L_(opt) is the optimal value of the largest distance. In the presentembodiment not only the distance L₁ and the distance L₂ but also(L₁/2),(L₂/2), . . . , (L_(n−1)/2) range all from 95% to 105% of theoptimal value.

Such an electrode for electrochemical devices 10 elicits the same effectas that of the first embodiment. Needless to say, the electrode of thesecond embodiment and the third embodiment may be provided as aplurality of electrodes, as in the fourth embodiment.

Electrochemical Device

An electrochemical device using the above-described electrode 10 isexplained next with reference to FIGS. 5 and 6. The electrochemicaldevice explained herein uses the electrode for electrochemical devicesof the first embodiment, but may equally use the electrode forelectrochemical devices of any of the other embodiments.

An electrochemical device 100 illustrated in FIGS. 5 and 6 comprises acase 50, a wound body 30 and an electrolyte solution, omitted in thefigure, held in the case and impregnating the wound body 30.

The case 50 seals the wound body 30 and prevents intrusion of air andmoisture into the interior of the case. The material used in the case 50may be, for instance, a synthetic resin such as an epoxy resin, alaminate film in which a metal sheet of aluminum or the like is coatedwith a resin. The lead 15 of the wound body 30 protrudes out of the case50.

The electrolyte solution (not shown) fills the inner space of the case50. Part of the electrolyte solution is contained in the interior of anelectrode 10, an electrode 10 and a separator 20.

In the case of a lithium-ion secondary battery, for instance, theelectrolyte solution used may be, for instance, a nonaqueous electrolytesolution in which a lithium salt is dissolved in an organic solvent.Examples of the lithium salt include, for instance, LiPF₆, LiClO₄,LiBF₄, LiAsF₆, LiCF₃SO₃, LiCF₃CF₂SO₃, LiC(CF₃SO₂)₃, LiN(CF₃SO₂)₂,LiN(CF₃CF₂SO₂)₂, LiN(CF₃SO₂)(C₄F₉SO₂) and LiN(CF₃CF₂CO)₂.

In the case of an electric double-layer capacitor, for instance, therecan be used an electrolyte solution obtained by dissolving a quaternaryammonium salt such as tetraethylammonium tetrafluoroborate (TEA⁺BF₄ ⁻)or triethylmonomethylammonium tetrafluoroborate (TEMA⁺BF₄ ⁻) in anorganic solvent.

These salts may be used singly or in combinations of two or more. Theelectrolyte solution may form a gel through addition of a polymer or thelike.

Known solvents used in electrochemical devices may be employed as theorganic solvent. Preferred examples thereof include, for instance,propylene carbonate, ethylene carbonate and diethyl carbonate. Theseorganic solvents may be used singly or in mixtures of two or more atarbitrary mixing ratios.

The wound body 30 is obtained by winding, in the longitudinal direction,a pair of the above-described electrodes for electrochemical devices 10,10, in such a manner that a separator 20 is interposed between theelectrodes for electrochemical devices 10, 10.

Specifically, for instance, a stack resulting from stacking an electrode10/separator 20/electrode 10/separator 20 is wound into a tubular form,starting form one end of the stack, to yield the wound body 30illustrated in FIG. 5, having a substantially tubular cross section.Also, the above-described stack may be wound several times, startingfrom one end, while bending the stack into a flat form, to yield thewound body 30 illustrated in FIG. 6, having a substantially oval crosssection.

The position at which the leads 15 protrude may lie in the samedirection between electrodes, as illustrated in FIG. 6, or in mutuallyopposing directions between electrodes, as illustrated in FIG. 5.

The separator 20, which provides electric insulation between theelectrodes for electrochemical devices 10, 10, is an electricallyinsulating porous member. The material of the separator is notparticularly limited, and there may be used various separator materials.Examples of electrically insulating porous members include, forinstance, a stretched film of a single-layer or a multilayer filmcomprising polyethylene, polypropylene or a polyolefin, or of a mixtureof the foregoing resins, or, alternatively, a fibrous nonwoven fabriccomprising at least one constituent material selected from the groupconsisting of cellulose, polyester and polypropylene.

In such an electrochemical device there must be used an electrode forelectrochemical devices in which L_(a) and L_(b), or L_(a), L_(b),(L₁/2), (L₂/2), . . . and (L_(n−1)/2) are as prescribed above. Bothimpedance and leakage current are small in such an electrochemicaldevice.

The present invention is not limited to the above embodiments, and mayaccommodate various modifications. In the above embodiments, forinstance, the collector is shaped as an elongated plate, but thecollector need only be a thin a long member, i.e. need only have alongitudinal direction. The collector may thus be shaped, for instance,as an elongated wire.

The electrochemical device is not limited to batteries such aslithium-ion secondary batteries, or to electric double-layer capacitors,and may also be realized in, for instance, electrolytic capacitors orthe like.

EXAMPLES Electric Double-Layer Capacitor (EDLC): Examples A1 to A3,Comparative Examples A1 and A2

A coating material was prepared by mixing activated carbon particles, asthe active material, and PVDF as the binder, to a ratio active material:binder=70:30; then N-methyl pyrrolidone was added to the obtainedmixture, and the whole was kneaded. The coating material was coated,using a doctor blade, onto both faces of 30 μm aluminum foil, except atthe portion intended for lead placing. The resulting coating films werethen dried. The aluminum foil having formed thereon the coating filmswas then punched into a rectangle, and then a lead having a width A of 2mm, a length of 25 mm and a thickness of 0.1 mm was ultrasonicallywelded to the uncoated portion of the collector, as illustrated in FIG.1, to yield a pair of electrodes for an electric double-layer capacitor.The length Lo of the collector in the longitudinal direction, anddistances L_(a), L_(b) from the ends of the collector to the lead wereset as given in FIG. 7 for the various examples and comparativeexamples. The width W₀ of the collector was 10 mm.

Both faces of one of the obtained electrodes were covered with anonwoven fabric of regenerated cellulose (thickness 30 μm), after whichthe electrode was disposed opposite the other electrode, and theresulting stack was wound into a tubular shape, from one end of thestack. The wound stack was fitted into a case made of aluminum laminatefilm, the lead was drawn out through the opening of the laminate film,and the opening was thermocompression-bonded, flanking the lead portion.An electrolyte solution for electric double-layer capacitors was pouredonto the stack through the last remaining opening of the outer bag ofaluminum laminate in which the stack was placed. The remaining openingwas then sealed through vacuum thermocompression bonding, followed byaging, to yield the various electric double-layer capacitors. Theelectrolyte solution was a solution of tetraethylammoniumtetrafluoroborate (TEA⁺BF₄ ⁻) as the electrolyte, dissolved in propylenecarbonate (PC), as an organic solvent. The electrolyte concentration inthe electrolyte solution was 1.0 mol/L.

Electric Double-Layer Capacitor: Examples A4 to A5, Comparative ExamplesA3 and A4

Electric double-layer capacitors were obtained in the same way as inExample 1, but using herein 17 μm-thickness copper foil instead ofaluminum foil, with L₀, L_(a) and L_(b) set as in FIG. 7.

Lithium-Ion Secondary Battery (LIB): Examples B1 to B3, ComparativeExamples B1 to B4

Cathode electrodes were manufactured in accordance with the procedurebelow. Firstly there were prepared LiCoO₂ as a positive electrode activematerial, acetylene black as a conduction enhancer and polyvinylidenefluoride (PVdF) as a binding agent. These were mixed and dispersed in aplanetary mixer to relative weights of positive electrode activematerial: conduction enhancer: binding agent=90:6:4. Thereafter, theviscosity of the resulting dispersion was adjusted through addition of asuitable amount of NMP, as a solvent, to yield a slurry-like cathodecoating liquid (slurry).

Aluminum foil (thickness 20 μm) was prepared next as the collector, andthe cathode coating liquid was coated to an active material carryingamount of 1.0 mg/cm², onto both faces of the aluminum foil, except atthe portion planned for lead welding, using a doctor blade. This wasfollowed by pressing using a calender roll, to a porosity of 28% of thecoated active material layers. The pressed product was punched into arectangle, to yield the cathode electrode. The distances L₀, L_(a),L_(b) were set as in FIG. 7, and the width W₀ was 10 mm.

Anode electrodes were manufactured next in accordance with the procedurebelow. Firstly there were prepared natural graphite as a negativeelectrode active material and polyvinylidene fluoride (PVdF) as abinding agent. These were blended, mixed and dispersed in a planetarymixer to relative weights of negative electrode active material: bindingagent=95:5). Thereafter, the viscosity of the resulting dispersion wasadjusted through addition of a suitable amount of NMP, as a solvent, toyield a slurry-like anode coating liquid. Copper foil (thickness 17 μm)was prepared next, and the anode coating liquid was coated to an activematerial carrying amount, on the anode electrode, of 3.0 mg/cm², ontoboth faces of the copper foil, except at the portion planned for leadwelding, using a doctor blade. This was followed by pressing using acalender roll, to a porosity of 30% of the active material layers of theanode electrode. The pressed product was punched into a rectangle, toyield the anode electrode. The distances L₀, L_(a), L_(b) were set as inFIG. 7, and the width W₀ was 10 mm.

Both faces of one of the obtained electrodes were covered with asingle-layer polyethylene porous film (thickness 12 μm), as a separator,after which the electrode was disposed opposite the other electrode, andthe resulting stack was wound into a tubular shape, from one end of thestack. The wound stack was fitted into a case made of aluminum laminatefilm, the lead was drawn out through the opening of the laminate film,and the opening was thermocompression-bonded, flanking the lead portion.An electrolyte solution for lithium-ion secondary batteries was pouredonto the stack through the last remaining opening of the outer bag ofaluminum laminate in which the stack was placed. The remaining openingwas then sealed through vacuum thermocompression bonding, followed byaging, to yield the various lithium-ion secondary batteries.

As the electrolyte for lithium-ion secondary batteries there was used anelectrolyte obtained by dissolving LiPF₆, to a concentration of 1.5mol/dm³, in a solvent resulting from mixing propylene carbonate (PC),ethylene carbonate (EC) and diethyl carbonate (DEC), to a volume ratioof 2:1:7, respectively. To 100 parts by weight of the resulting solutionthere were further added 3 parts by weight of 1,3-propane sultone.

Evaluation of the electric double-layer capacitors and lithium-ionsecondary batteries

The electric double-layer capacitors and lithium-ion secondary batteriesof the examples and comparative examples were measured for impedance andleakage current. The values are illustrated in FIG. 7. In the electricdouble-layer capacitors, impedance was measured in the discharged state,while leakage current was measured after charging at 4 V for 1 hour. Inthe lithium-ion secondary batteries, impedance was measured in a stateresulting from discharge to 3 V, while leakage current was measuredafter charging at 4 V for 1 hour.

In Examples A1 to A3, relating to electric double-layer capacitors usingcollectors made of aluminum, there was achieved an impedance of lessthan 100 mΩ. In Examples A4 and A5, relating to electric double-layercapacitors using collectors made of copper, there was achieved animpedance of less than 60 mΩ. In Examples B1 to B3, relating tolithium-ion secondary batteries, there was achieved an impedance of lessthan 130 mΩ. A leakage current no greater than 20 mA/h was achieved inall the examples.

1. An electrode for an electrochemical device, comprising: an elongatedcollector; a lead provided halfway along a longitudinal direction ofsaid collector; and an active material layer provided on said collector,wherein when L_(a) (m) is a distance from one end of said collector, inthe longitudinal direction, up to said lead, L_(b) (m) is a distancefrom the other end of said collector, in the longitudinal direction, upto said lead, and ρ (Ωm) is a resistivity of said collector at 25° C.,where L_(opt) (m) being 1.9×10⁶ρ, the L_(a) (m) and L_(b) (m) are from0.95 L_(opt) to 1.05 L_(opt) respectively.
 2. An electrode for anelectrochemical device, comprising: an elongated collector, n leads (nbeing an integer equal to 2 or greater) provided spaced apart from eachother in said collector along a longitudinal direction of saidcollector; and an active material layer provided on said collector,wherein when L_(a) (m) is a distance from one end of said collector, inthe longitudinal direction, up to a lead closest to said one end, L_(b)(m) is a distance from the other end of said collector, in thelongitudinal direction, up to a lead closest to said other end, L₁, L₂,. . . , L_(n−1) (m) are distances between adjacent leads, and ρ (Ωm) isa resistivity of said collector at 25° C., where L_(opt) (m) being19×10⁶ρ, the L_(a) and L_(b) are from 0.95 L_(opt) to 1.05 L_(opt)respectively, and (L₁/2), (L₂/2), . . . , (L_(n−1)/2) respectively rangefrom 0.95 L_(opt) to 1.05 L_(opt).
 3. An electrochemical device,comprising a pair of electrodes, wherein both electrodes are theelectrode for electrochemical devices according to claim
 1. 4. Anelectrochemical device, comprising a pair of electrodes, wherein bothelectrodes are the electrode for electrochemical devices according toclaim 2.